In computer networks, it is necessary for applications to access files located on network servers. When an application tries to access a file over a network, a file system call 109 is sent by the application, which resides in a client, to a network server. Microsoft® (MS) networks have components at the file system level. Microsoft® also has proprietary protocols at the file system level to help get the files over the network. Protocols define how computers identify one another on a network, the format by which the data is sent, how the data should be processed once it reaches its final destination and procedures for handling lost or damaged transmissions or “packets.”
File system calls, in MS-networks, go through an installable file system manager (IFSMGR), a Microsoft® component. The IFSMGR handles all calls from all of the applications—including 32 bit, 16 bit, and DOS applications. Multiple file system providers may be installed on the system. One file system provider is a default file system provider, which is a Microsoft® network redirector. Each call is routed by the IFSMGR to the MS-network redirector, which constructs a network request and sends the request over the network. The MS-network redirector also encodes requests and decodes responses. The MS-network redirector works serially, which means that the redirector will send one request, wait for a response, and once it receives the response sends the next request. This system of processing file system calls is synchronous with application requests as well. In synchronous communications, each party is required to wait a specified interval before speaking—in contrast to asynchronous communications where both parties can talk whenever they like.
Microsoft® uses a Server Message Block (SMB) protocol. SMB is a message format used by DOS and Windows to share files, directories and services. The MS-network redirector encodes the file system request into SMB format and sends it through Network Basic Input Output System (NetBIOS) on Transmission Control Protocol/Internet Protocol (TCP/IP). NetBIOS is an application programming interface that augments DOSBIOS by adding special functions for Local Area Networks (LANs). Thus, the actual transfer of data is done over TCP/IP.
A characteristic of TCP/IP is that every TCP packet must be acknowledged, which creates traffic in the reverse direction. In protocols having slotted architecture, each slot may have two nodes, node A and node B, such that when node A is transmitting, node B is receiving and vice versa. Therefore, when TCP/IP is used to transmit data, some bandwidth must be allocated in the slot for the reverse channel to accommodate the traffic in the reverse direction, which lowers the amount of bandwidth that can be allocated for the forward channel.
Thus, network performance is lowered by the requirement of bandwidth for a backward channel and the system of processing file system calls being synchronous with application requests.